[ruby-core:109540] [Ruby master Bug#18751] Regression on master for Method#== when comparing public with private method

["Eregon (Benoit Daloze)" <noreply@ruby-lang.org>]

Issue #18751 has been updated by Eregon (Benoit Daloze).


We discussed this at the dev meeting.
@ko1 said Method#== should be "is it the same definition?".
I agree, I'll take a look at this with #18729 and #18435.

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Bug #18751: Regression on master for Method#== when comparing public with private method
https://bugs.ruby-lang.org/issues/18751#change-98711

* Author: Eregon (Benoit Daloze)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.2.0dev (2022-04-23T02:59:20Z master e142bea799) [x86_64-linux]
* Backport: 2.7: DONTNEED, 3.0: DONTNEED, 3.1: DONTNEED
----------------------------------------
This script repros:
```ruby
class C
  class << self
    alias_method :n, :new
    private :new
  end
end

p C.method(:n) == C.method(:new) # => true

puts
p C.method(:n) == Class.method(:new) # => false
p C.method(:n) == Class.method(:new).unbind.bind(C) # => true

puts
p C.method(:new) == Class.method(:new) # => false
p C.method(:new) == Class.method(:new).unbind.bind(C) # => true, BUT false on master
p C.method(:new) == Class.instance_method(:new).bind(C) # => true, BUT false on master
p [C.method(:new), Class.instance_method(:new).bind(C)] # => [#<Method: #<Class:C>(Class)#new(*)>, #<Method: #<Class:C>(Class)#new(*)>]
```

So this prints the expected results on 2.7.5, 3.0.3, 3.1.1 but not on master, which seems a regression.
Notably this breaks the pattern discussed in https://bugs.ruby-lang.org/issues/18729#note-5, and it means there is no way to find out if two methods share the same "definition/logic/def", which is a big limitation.



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